You may be right about Hubris's worldgen, in which case chances are a custom mod would be required to do this. Unless of course one already exists, in which case we're good to go. I've also seen Rivers that are clear of taint, but they dry up as Flux Goo from all the trees around flows in and destroys the water. However, the biome doesn't change no matter how many Tainted nodes are near it, and in fact I've so far found no way to convert Rivers or Beaches to Tainted Lands. Not that I've tried too hard, since I've been busy trying to actually progress in the game.
As for the Blightfall map, I'm pretty sure how he did that was by using natural worldgen to make the world, and then overriding ALL biomes with Tainted Lands except for some select areas. He then probably waited a bit in all the sections to make the Taint progress somewhat and make it look the way it does. I feel like if the worldgen for Hubris did that it would be a lot more interesting, though you'd have to code it separately to convert the world to Taint after everything has generated. If Oceans and Rivers are needed to remain untainted that could also be part of the code but invincible beaches and those other technical biomes could all be tainted this way.
